1. Field of the Invention
This invention concerns improvements in or relating to the friction welding of components.
In particular, the invention concerns a method for the manufacture or repair of a BLISK by linear friction welding.
2. Description of the Related Art
The two most commonly used methods for manufacturing BLISKs are machining from solid and attaching separately made blades onto a disk by friction welding. A further operation to remove upset or welding flash may be required as part of a finish machining procedure. Machining from solid is expensive and inevitably results in an unacceptable wastage of material, especially in the case of larger BLISKs. The method of present interest, in any case, can be employed as a repair technique to replace individual blades irrespective of whether a BLISK was manufactured from solid or fabricated using the same method. However, friction welding of blades onto a disk permits the blade and disk properties to be optimised, such as in a cast blade and a forged disk, and the use of dissimilar materials.
Methods for fabrication or repair of integrally bladed rotor assemblies involving providing a projecting stubs on the disk periphery are described in EP 376,874 (equivalent U.S. Pat. No. 4,873,751) and GB 2,218,016 (equivalent U.S. Pat. No. 4,883,216). Although the shape or configuration of the projecting stub is mentioned in both documents the top surface of the stub, which forms a joint surface, is not considered. The drawings contained in these patent specifications invariably show a planar top surface on the stub. However, EP 376.874 (and equivalents) does not mention linear friction welding as a possible joining technique, and GB 2,218,016 mentions it only as one of a possible list of techniques for heating the joint without any ensuing discussions whatsoever. In all instances, however, a weld force is shown acting "downwards" urging the new blade onto the stub in a generally radial direction. In order to avoid lateral displacement of one part relative to another in the joint or other distortion effects there is good reason to generate the weld joint surface in a flat plane perpendicular to a radial direction containing the applied weld force.
Gas turbine engine rotors are not normally designed with a cylindrical gas washed surface, thus a disk peripheral surface is almost always convergent, in one axial direction or the other, with the disk rotational axis. Furthermore, this surface may also be concave or convex and in some fan and low pressure compressor stages utilizing wide chord blades having a significant circumferential length the footprint of the blade on the disk surface is three dimensional and complex.
In friction welding the disk is clamped and, for example, a location on the disk periphery is presented to a welding station. At the welding station a blade clamped in a second item of tooling is rubbed against the disk surface to generate frictional heat at the interface. When a predetermined loss of length is achieved the blade is brought suddenly to a halt at a precisely defined location on the disk and is pressed against the disk for a short time to create the weld. When the assembly has cooled flash at the interface is removed and any required finish machining operations are carried out. If an airfoil has been damaged, e.g. by foreign object ingestion into an engine core, it is possible to remove a damaged blade and then to insert a replacement blade by the friction welding technique, thus avoiding the necessity of replacing a damaged BLISK in its entirety.